Putting an old HD in a new PS3 without formatting

[ghettoglamour]

you need a 2,5 inch SATA HDD. 50$ should be enough for 500gb, I don't know the prices in your country though.
then, you need to back up your data onto an external HDD from your PS3. After that you put in the new HDD and format it. When it's done you only need to copy from your backup onto your new formatted HDD.